As an apparatus for classifying particles suspended in a gas by their electric mobilities, one is disclosed in the Journal of Aerosol Science, Vol. 16, pp. 443-452, "Aerosol Classification by Electric Mobility" by E. O. Knutson and K. T. Whitby (Reference 1).
The prior art classifying apparatus per se can only classify particles by their electric mobilities. However, by connecting the condensation nucleus type counter device disclosed in "Aerosol Technology" (Wiley Interscience 1982), p. 262 by W. C. Hinds (Reference 2) to the aforementioned apparatus for classifying particles by their electric mobilities and counting the number of the classified particles at various electric mobility values, it is possible to measure electric mobility distribution with high precision.
In the Journal of Aerosol Science Vol. 9, pp. 41-54 (1978), "Determination of the Aerosol Size Distribution from the Mobility Distribution of the Charged Fraction of Aerosol" by W. A. Hoppel (Reference 3), there is described a data processing method for converting the electric mobility distribution obtained as described above into particle size distribution.
However, the data processing method relates to a method for solving a problem falling in the category of so-called inverse problems. Owing to the nature of such problems, there are cases where no solution exists and where the uniqueness or stability of a solution is not assured. For these reasons, there are some cases that fail to measure particle size distribution or give rise to a large error in the particle size distribution measured.
Examples of methods for directly measuring particle size distribution of particles suspended in a gas include the light-scattering method using a light-scattering type automatic particle counter prescribed by JIS-B-9921 (Reference 4), the method using an impactor, described in "Applied Aerosol Technology" (Yokendo, 1984), p. 262 by Mikiji Takahashi (Reference 5) and the aerosol beam method described in "Applied Aerosol Technology" (Yokendo 1984) p. 264 by Mikiji Takahashi (Reference 6).
However, these methods for the direct measurement of particle size distribution have difficulty in measuring a particle size distribution with high precision.
In view of the above, an object of the present invention is to provide a measuring method and a measuring apparatus that can measure particle size distribution of particles suspended in a gas with precision higher than that obtained in the conventional methods of measuring particle size distribution by obtaining particle sizes from the electric mobility and number of charges of individual particles without using any analytical means.